Exploding mirror for optical viewing system

ABSTRACT

An exploding mirror for an optical viewing system which will partially self-destruct when a laser beam of a minimum predetermined energy density impinges thereon. Using an epoxy encapsulation method, an explosive charge is placed adjacent a thin film mirror on a glass slide. The opposite side of the mirror is part of the optical sight path of the viewing system. A laser beam of sufficient energy density will cause the explosive charge to detonate, thus blowing out a critical section of the mirror and disrupting the optical sight path, thereby protecting the viewer.

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[72] inventors Richard J.l CM

f KH JPATENTS 21] A I No 3223?; 3,152,215 10/1964 Barstow m1. 350/160 ff0J8 1968 3,213,752 10/1965 Ruderman 350/160X Patented May 18,19713,414,838 12/1968 DeMent 350/288(UX) 73 Assignee the United States ofAmerica as represented Primary Ex mi r-R n y D- B n rhy the Secretary ofthe Army Assistant Examiner-Daniel C. Kaufman Attorney's-Harry M.Saragovitz, Edward J. Kelly, Herbert Berl and J. D. Edgerton ABSTRACT:An exploding mirror for an optical viewing 54] EXPLODING MIRROR FOROPTICAL VIEWING system wh1ch will part1ally self-destruct when a laserbeam of a SYSTEM fimlmum predetermlneii tenergyudgzsity 1m i1ngestllliereon. smg an epoxy encapsu a 10n me an exp os1ve c arge 1s4chims4nnwmg Figs placed adjacent a thin film mirror on a glass slide.The op- [52] U.S. Cl 350/ 160, posite side of the mirror is part of theoptical sight path of the 350/288 viewing system. A laser beam ofsufiicient energy density will [51] Int.Cl. G02b 5/08 cause theexplosive charge to detonate, thus blowing out a [50] Field of Search350/l60, critical section of the mirror and disrupting the optical sight288 path, thereby protecting the viewer.

WW I 4% I f9 1 (mm A PATENTEU HAY18I9H 3578.842

INVENTORS RICHARD J. HOLLAND TIMOTHY J. KILDUFF ZOLTAN G SZTANKAY BY2A1; i- M 6, wJ/

I ATT RNEYS RIGHTS OF THE GOVERNMENT The invention described herein maybe manufactured, used, and licensed by or for the United StatesGovernment for governmental purposes without the payment to us of anyroyalty thereon.

BACKGROUND OF THE INVENTION Devices using lasers have recently beendeveloped for communications and other military purposes, such as rangefinders. With the use of laser devices, there is a need for effectiveprotection of personnel against the harmful effects that excessive laserenergy can have on their vision. This can occur when personnel usingsighting devices, such as periscopes, may inadvertently intercept alaser beam originating from friendly or enemy sources.

An optical viewing system for protection against laser beams isdisclosed in US. Pat. application, Ser. No. 457,545, filed May 20, I965by Hans W. Kohler et al., and assigned to the assignee of the instantapplication. The system of the aforementioned application splits theincoming light into two beams, the see beam and the burn beam." The seebeam" is delayed before reaching the exploding mirror where it would bereflected from its mirror side. The bum beam" is immediately incident onthe exploding mirror on its explosive side. When a laser beam ofsufficient energy density is received by the system, the bum beam"causes the exploding mirror to destroy a critical section of itself,thus disrupting the transmission of the see beam" before it reaches theoperators eye. The problem in making a working embodiment of such asystem has been to develop a disruptive element which will disrupt thepath of the see beam" by destroying a critical section of the reflectivesurface in a period of 25 nanoseconds or less when struck by a laserbeam of focused energy density of IO .l/cm. or greater.

Prior attempts to design disruptive elements to meet the systemrequirements have been proposed by D. Hartter in FEASIBILITY OFEXPLOSIVE MIRRORS FOR THE LASER BEAM DISRUPTER (Conf) 25 Jan. 65, HDLReport R9l065-CI and by D. Hartter, .I. Boyd and Z. Sztankay, in LASERINITIATION OF THIN EXPLOSIVE WAFERS (U) 1968 (Conf.), HDL TechnicalReport TR-l386. In the first report, Hartter proposes an explosive filmadjacent to a thinfilm mirror and in the second report the authorsdisclose a pressed wafer of explosive material adjacent to a thin-filmmirror and confined by series of thin plastic films. During thedevelopment of the explosive film system, experimentation showed that ahigh density of the explosive was necessary in order to realize the fastinitiation times which were required. The exploding film mirrors werefound not to have the required density and were therefore unsatisfactoryfor the required system. While the design using a pressed wafer ofexplosive material with laminate structure did have the desired density,there was a problem of improper matching of layer thickness to chargethickness after constructing the confinement volume with the layeredplastic films. Another problem in constructing the latter device wascutting holes in the laminates to the exact profile of the thinexplosive wafer used.

It is therefore an object of this invention to provide a disruptiveelement to be used in an optical sighting device which will disrupt thesight path in a given period of time after being impinged upon by alaser beam of sufficient energy density.

An additional object of the invention is to provide a disruptive elementfor an optical viewing device which will protect the eyesight of anobserver using the viewing device from the harmful effects of laserradiation.

Still an additional object of the invention is to provide a method ofmaking an exploding mirror for an optical viewing system which willoperate within the designed criteria needed by the system in order toprotect against the hannful effects of laser radiation.

SUMMARY OF THE INVENTION Theaforementioned objects of our invention areachieved by a thin-film mirror deposited on a glass slide with anexplosive wafer placed adjacent to the thin-film mirror at a pointcorresponding to the area of the mirror upon which the opticalsight-path is focused. The explosive wafer and thin-film mirror aretightly encapsulated in a clear epoxy. The exploding mirror isconstructed by placing the glass slide with the thin-film mirror in amold, positioning the explosive wafer over the mirror and filling themold with epoxy. After removal from the mold the exterior surface of theepoxy is polished for transparency.

BRIEF DESCRIPTION OF THE DRAWINGS The specific nature of the inventionas well as other objects, aspects, uses, and advantages thereof willclearly appear from the following description and from the accompanyingdrawing, in which:

FIG. 1 illustrates the explod our invention.

FIGS. 2a, 2b, and 2c illustrate the method used to make an explodingmirror in accordance with our invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates an explodingmirror having a clear epoxy covering 10 encapsulating a glass slide 15with a thin-film mirror 20 deposited thereon. An explosive charge 13 issituated in between the thin-film mirror 20 and the epoxy covering 10directly adjacent to the center of the thin-film mirrored surface 20.The epoxy covering 10 is 30 to 50 mils thick and its top surface 11 isbuffed fiat so as to present a transparent surface to a laser beamapproaching along path 12. The glass slide 15 is approximately 6 milsthick and is also transparent to a light beam which approaches alongpath 17 and is reflected from the mirror 20 along path I8.

During operation of an optical viewing system utilizing the explodingmirror of FIG. I, such as the copending application previously referredto, the light entering the viewing system will directly approach theexploding mirror as a burn beam" along the light path 12 and a delayedbeam or see beam in the optical sight path will approach along the path17 to be reflected by mirror 20 along path 18. The mirror 20 will bereflective as long as the burn beam" entering along path 12 does notdetonate the exploding charge I3. If the energy density of the incominglight to the viewing system becomes excessive, i.e. a laser beam isencountered of sufficient energy density, the burn beam will cause theexplosive charge 13 to ing mirror in accordance with detonate and theensuing explosion will destroy the thin-film mirror 20 and part of theglass slide 15, thereby disrupting the optical sight path 17 and 18.This will interrupt the see beam" and prevent any excessive laser energyfrom reaching the eye of an observer.

FIGS. 2a, 2b, and 2c illustrate the method used to construct theexploding mirror shown in FIG. 1. In FIG. 2a, a mold 25 is fabricatedfrom polystyrene by a well-known vacuum thermoform process over arectangular steel block 24 on which is positioned the glass slide 15having the mirror 20 deposited thereon. The glass slide I5 is orientedso that the mirrored surface 20 is between the slide 15 and the steelblock 24. The upper surface 27 of the glass slide I5 is coated withsilicone grease (not shown) before the thermo-form process to allow easyremoval of the completed mirror from the mold 25. After shaping thepolystyrene, the steel block 24 is removed and the mold 25 is ready forplacement of the explosive charge.

In FIG. 2b, a small amount of silicone oil (not shown) is centrallyplaced on the mirrored surface 20 and the charge 13 is set snugly intothe oil in the center of the thin-film mirrored surface 20. Epoxy 10 isthen poured over the explosive charge 13, the mirror 20, and the glassslide 15 so as to fill the hollow space in the mold 25 as shown in FIG.2c. The silicone oil is used to prevent the epoxy 10 from seepingbetween the mirror 20 and charge 13. Such seepage might hinderdestruction of the mirror 20 after detonation of the explosive charge13. When the epoxy is fully cured the exploding mirror assembly isremoved from the mold 25, and the upper surface of the epoxy 11 can thenbe ground flat on fine emery and buffed clear to a windowlikeappearance. The exploding mirror is now ready for operation as describedabove.

Tests were run on exploding mirrors constructed in accordance with theforegoing method at the Harry Diamond Laboratories in Washington, DC.The experiments performed recorded delay times ranging between and 30nanoseconds for an incident igniting beam of 10 J/cm energy density Itis apparent that these results are well within the stipulatedrequirements for an optical viewing system as described.

It will be apparent that the embodiments shown are only exemplary andthat various modifications can be made in construction and arrangementwithin the scope of the invention as defined in the appended claims.

We claim:

1. An exploding mirror for an optical viewing system incorporating alaser beam comprising:

a. a first light path;

b. a second light path;

c. reflecting means to reflect light transmitted by said second lightpath and not by said first light path; and

d. explosive charge disrupter means responsive to the direct impingementof light thereon to destroy said reflecting I211 3;:s m response tolight transmitted by said filSLllgllt 2. The exploding mirror of claim 1wherein said exploding charge is positioned adjacent to said reflectingmeans.

3. The exploding mirror of claim 2 wherein said reflecting means is athin-film mirror deposited on glass.

4. The exploding mirror of claim 3 wherein said explosive charge andsaid thin-film mirror are encapsulated in epoxy, the light transmittedby said first light path passing through the epoxy before impinging uponsaid explosive charge.

1. An exploding mirror for an optical viewing system incorporating alaser beam comprising: a. a first light path; b. a second light path; c.reflecting means to reflect light transmitted by said second light pathand not by said first light path; and d. explosive charge disruptermeans responsive to the direct impingement of light thereon to destroysaid reflecting means in response to light transmitted by said firstlight path.
 2. The exploding mirror of claim 1 wherein said explodingcharge is positioned adjacent to said reflecting means.
 3. The explodingmirror of claim 2 wherein said reflecting means is a thin-film mirrordeposited on glass.
 4. The exploding mirror of claim 3 wherein saidexplosive charge and said thin-film mirror are encapsulated in epoxy,the light transmitted by said first light path passing through the epoxybefore impinging upon said explosive charge.